The long-term goal of this research is to use an animal model to identify genetically controlled molecular mechanisms that determine resistance and susceptibility to viral- induced abnormalities in pulmonary structure and function that result in persistent airway obstruction and hyperresponsiveness (features of asthma). These functional abnormalities have been detected in children following viral bronchiolitis in infancy caused by respiratory syncytial virus and parainfluenza virus. Parainfluenza type 1 (Sendai) virus infection in genetically-susceptible (BN) and resistant (F344) rats is being used as an animal model of lower respiratory illness during infancy. The experimental hypothesis being tested is that viral bronchiolitis during early life in genetically- susceptible individuals induces accentuated airway cytokine gene expression that results in alterations in bronchiolar growth and in airway inflammatory cell number and function to induce persistent airway obstruction and hyperresponsiveness. The specific aims of the proposed research are: l) To use Northern analysis and in situ hybridization to determine whether virus-susceptible BN rats have increased cytokine gene expression of mRNA for transforming growth factor-beta1 (TGF-beta1), tumor necrosis factor-alpha (TNF-alpha), interleukin-3, and/or stem cell factor (SCF) following Sendai virus infection and prior to bronchiolar growth abnormalities and hyperresponsiveness; 2) To use Western blot analysis and lymphocyte sub-set immuno-cytochemistry to determine whether the enhanced susceptibility of BN rats to Sendai virus-induced growth abnormalities is due to less efficient antiviral immune response (CD8 lymphocytes and anti- HN antibody) than in F344 rats; 3) To characterize virus-induced alterations in bronchiolar and bronchiolar mast cell eicosanoid metabolism with high performance liquid chromatography and enzyme-linked immunoassay; and 4) To use breeding studies to determine whether resistance and susceptibility in rats to virus-induced airway abnormalities and hyperresponsiveness are inherited in a polygenic or simple Mendelian pattern. The long-term goal of this research approach will be to use simple sequence length polymorphisms and computer analysis to identify genomic segments containing loci that control susceptibility to virus- induced airway abnormalities.